Damage Threshold of Normal Rat Brain in Photodynamic Therapy

Normal brain tissue response to photodynamic therapy (PDT) must be quantified in order to implement PDT as a treatment of brain neoplasm. We therefore calculated the threshold for PDT-induced tissue necrosis in normal brain using Photofrin (porfimer sodium, Quadralogic Technologies Inc., Vancouver, BC) as the photosensitizer. The absolute light fluence-rate distribution for superficial irradiation and effective attenuation depth were measured in vivo using an invasive optical probe. Photosensitizer uptake in cerebral cortex was measured with chemical extraction and fluorometric analysis. Photodynamic therapy-induced lesion depths at various drug dose levels were measured as a biological end point. The PDT threshold for normal brain necrosis was calculated as in the magnitude of 10¹⁶ photons/cm³. Thus normal rat brain is extremely vulnerable to PDT damage. This suggests that extra precautions must be exercised when PDT is used in brain.     

电解质模型流体的Monte Carlo分子模拟

采用正则系综Monte Carlo分子模拟方法,模拟得到了一系列状态条件下1：1 价和2：2价对称电解质模型流体的径向分布函数、构型能和压缩因子的“机器实验 数据”,这些数据对构筑电解质溶液的新参考流体具有重要意义。模拟过程中,电 解质溶液被简化为硬球离子和硬球点偶扳子的混合物,离子—离子、离子—偶极和 偶极—偶极长程位能计算采用了Ewald求和方法。最后,对离子—偶极子混合物的 结构和热力学性质与体系温度、密度和浓度的关系进行了分析和讨论。     

Monte Carlo Simulation of Band Texture Formation in Macroscopically Oriented Semirigid Polymer System

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Model Discrimination in Copolymerization Using the Sequential Bayesian Monte Carlo Method

The authors have introduced and extended the sequential Bayesian Monte Carlo model discrimination (SBMCMD) method described in previous studies by Masoumi et al. for the purpose of discriminating between mechanistic models via designed experiments. The features of the Markov Chain Monte Carlo methods utilized in SBMCMD allow this method to work with a wide range of nonlinear models. Here, SBMCMD has been applied to simulated copolymerization systems to compare its performance with other statistical discrimination methods used in previous studies by Burke et al. In addition, the Hsiang and Reilly method has been reapplied to the same copolymerization systems to address questions arising from previous work on this subject. The results of applying the SBMCMD method show that it is possible to choose the best model correctly with fewer experiments compared to the previously studied methods. Results also confirm that copolymer composition data do not provide enough information to discriminate between terminal and penultimate data.

     

Local Photodynamic Therapy Reduces Tissue Hyperplasia in an Experimental Restenosis Model

Abstract— Local photodynamic therapy may have potential in preventing myointimal hyperplasia after angioplasty. In this study, the effect of photodynamic therapy was evaluated in an experimental model of restenosis. Standardized unidirectional arterial injury with a directional atherectomy catheter was performed in porcine arteries. Animals were randomly allocated to four groups: group 1, unidirectional injury only; group 2, injury followed by local delivery of photosensitizer; group 3, injury followed by local exposure to monochromatic light; and group 4, where injury was followed by local drug delivery of photosensitizer and subsequent exposure to light (photodynamic therapy). Seven, 14 or 21 days after treatment, all experimental vessels were excised, fixed and processed for histology. An inflammatory and myoproliferative response was observed after injury in vessels from groups 1, 2 and 3. In group 4, after injury followed by photodynamic therapy, the myoproliferative response was significantly reduced. Thus, in this study, tissue hyperplasia after unidirectional injury was effectively suppressed by photodynamic therapy.     

Antagonistic Effects of Endogenous Nitric Oxide in a Glioblastoma Photodynamic Therapy Model

Gliomas are aggressive brain tumors that are resistant to conventional chemotherapy and radiotherapy. Much of this resistance is attributed to endogenous nitric oxide (NO). Recent studies revealed that 5‐aminolevulinic acid (ALA)‐based photodynamic therapy (PDT) has advantages over conventional treatments for glioblastoma. In this study, we used an in vitro model to assess whether NO from glioblastoma cells can interfere with ALA‐PDT. Human U87 and U251 cells expressed significant basal levels of neuronal NO synthase (nNOS) and its inducible counterpart (iNOS). After an ALA/light challenge, iNOS level increased three‐ to fourfold over 24 h, whereas nNOS remained unchanged. Elevated iNOS resulted in a large increase in intracellular NO. Extent of ALA/light‐induced apoptosis increased substantially when an iNOS inhibitor or NO scavenger was present, implying that iNOS/NO was acting cytoprotectively. Moreover, cells surviving a photochallenge exhibited a striking increase in proliferation, migration and invasion rates, iNOS/NO again playing a dominant role. Also observed was a large iNOS/NO‐dependent increase in matrix metalloproteinase‐9 activity, decrease in tissue inhibitor of metalloproteinase‐1 expression and increase in survivin and S100A4 expression, each effect being consistent with accelerated migration/invasion as a prelude to metastasis. Our findings suggest introduction of iNOS inhibitors as pharmacologic adjuvants for glioblastoma PDT.     

钯团簇形成和增长机理的Monte Carlo研究

利用Monte Carlo（MC）方法和Lennard-Jones加Axilord-Teller （LJ＋AT）势能函数,研究了气相中钯团簇的形成过程和增长机理.发现具有二十面体结构的Pd13团簇可以在气相中自发形成,较大的团簇通过在Pd13二十面体结构的表面添加原子组成四面体的方式形成.通过分析团簇结构和能量之间的关系,发现除了Pd13和Pd55以外,Pd19和Pd39团簇也具有五次对称性,都是比较稳定的结构.     

Understanding the Formation of Linear Olefin Block Copolymers with Dynamic Monte Carlo Simulation

Chain‐shuttling polymerization with dual catalysts has introduced a new class of polyolefins called olefin block copolymers (OBCs). A dynamic Monte Carlo model to describe the kinetics of chain‐shuttling copolymerization in a semi‐batch reactor is developed, and used it to study how the microstructure of OBCs with different numbers of blocks per chain evolves during polymerization. The model also describes how chain‐shuttling rate constants and concentration of chain‐shuttling agent affect populations of OBCs with different numbers of blocks per chain. These model predictions are useful to make OBCs with precisely designed microstructures.

     

The Effect of Fluence Rate on Tumor and Normal Tissue Responses to Photodynamic Therapy

Photodynamic therapy (PDT), carried out at low fluence rates, may enhance tumor response as well as affect treatment selectivity. We have studied the effects of fluence rate on the response of the murine radiation-induced fibrosarcoma (RIF) to PDT using Photofrin® (5 mg/kg). Tumor response was tested over a large range of fluence rates (10-200 mW/cm²) and fluences (25-378 J/ cm²). Low fluence rates were more efficient; -60 J/cm2 at 10 mW/cm² was needed to achieve the same tumor growth delay as -100 J/cm² at 150 mW/cm² and -150 J/cm2 at 200 mW/cm². Despite this increased efficiency, lower fluence rates still required longer treatment times for equivalent anti-tumor effects: 95 min for 57 J/cm² at 10 mW/cm²versus 11 min for 100 J/cm² at 150 mW/cm². Effects of fluence rate on the PDT toxicity to normal tissue were examined through the response of the murine (C311) foot to Photofrin® PDT. Treatment with conditions that produced equivalent tumor responses, i.e. 57 J/cm² at 10 mW/cm² and 100 J/cm² at 150 mW/cm², resulted in a more severe foot response at the higher fluence rate (median peak response: 0.9 at 10 mW/cm², 1.5 at 150 mW/cm²) with more time required for tissue to return to normal (8 days at 10 mW/cm², at least 30 days at 150 mW/cm²). However, when feet were treated with an equal fluence of 100 J/cm2 at various fluence rates, longer healing times accompanied the lower fluence rate treatments. Overall, this paper demonstrates that lower PDT fluence rates are associated with increased efficiency of tumor response. If this increased efficiency is accounted for by lowering treatment fluence, lower fluence rates also may result in a more favorable normal tissue response to treatment.     

Quantum Monte Carlo study of first-row atoms using transcorrelated variational Monte Carlo trial functions

The effect of using the transcorrelated variational Monte Carlo (TC-VMC) approach to construct a trial function for fixed node diffusion Monte Carlo (DMC) energy calculations has been investigated for the first-row atoms, Li to Ne. The computed energies are compared with fixed node DMC energies obtained using trial functions constructed from Hartree-Fock and density functional levels of theory. Despite major VMC energy improvement with TC-VMC trial functions, no improvement in DMC energy was observed using these trial functions for the first-row atoms studied. The implications of these results on the nodes of the trial wave functions are discussed.     

Reactive Monte Carlo and grand-canonical Monte Carlo simulations of the propene metathesis reaction system

The influence of silicalite-1 pores on the reaction equilibria and the selectivity of the propene metathesis reaction system in the temperature range between 300 and 600 K and the pressure range from 0.5 to 7 bars has been investigated with molecular simulations. The reactive Monte Carlo (RxMC) technique was applied for bulk-phase simulations in the isobaric-isothermal ensemble and for two phase systems in the Gibbs ensemble. Additionally, Monte Carlo simulations in the grand-canonical ensemble (GCMC) have been carried out with and without using the RxMC technique. The various simulation procedures were combined with the configurational-bias Monte Carlo approach. It was found that the GCMC simulations are superior to the Gibbs ensemble simulations for reactions where the bulk-phase equilibrium can be calculated in advance and does not have to be simulated simultaneously with the molecules inside the pore. The confined environment can increase the conversion significantly. A large change in selectivity between the bulk phase and the pore phase is observed. Pressure and temperature have strong influences on both conversion and selectivity. At low pressure and temperature both conversion and selectivity have the highest values. The effect of confinement decreases as the temperature increases.     

金属间化合物NiAl晶格模型的蒙特卡罗模拟

采用巨正则系综蒙特卡罗(GCMC)方法对NiAl合金晶格模型在1273 K温度下的点缺陷浓度和Al原子相对化学活度等进行计算, 并与实验数据及缺陷关联模型(DCM)的理论计算结果进行比较. 结果发现, 当Ni原子比大于0.475时, 晶格模型能很好地描述NiAl合金的行为; 当Ni原子比小于0.475时, 空位浓度高于0.05, 晶格模型相互作用参数须作适当修正. 研究指出GCMC能很好地模拟晶格模型的热力学性质, DCM在描述富Ni区域Al空位的热激发行为和富Al区域Ni空位分布的关联性方面有局限性.     

DFT-LDA pseudopotentials in quantum Monte Carlo

We investigate the portability of standard norm-conserving pseudopotentials outside the density functional theory-local density approximation (DFT-LDA) framework, i.e., their use and interpretation as electron-ion effective potentials in valence-only diffusion Monte Carlo simulations. While first-principles many-body pseudopotentials are not available in the literature yet, the use of approximate pseudopotentials in quantum Monte Carlo simulations is becoming widespread. Here we attempt a systematic analysis of the portability of norm-conserving pseudopotentials generated within DFT-LDA, focusing on a model many-body system, the two-electron valence-only ion. Our results indicate that the portability is good in most cases, hence the use of pseudopotentials in quantum Monte Carlo simulations is in general a reasonable approximation but suggest that in some cases this approximation may be relevant. © 1997 John Wiley & Sons, Inc.     

Monte Carlo Simulation of the Reactive Formation of Co‐Continuous Nanostructured Polymers

Structure formation during high‐temperature reactive blending of randomly functionalized poly‐disperse backbone polymers (such as polyethylene) with end‐functionalized graft polymers (such as polyamide 6) forming co‐continuous nanostructured microphases was investigated by means of MC simulations using the bond fluctuation algorithm. We compared reacted and non‐reacted systems under the same conditions. For the non‐reacted system at low temperatures, phase separation was observed. In the system with grafting reactions, macroscopic phase separation was inhibited even if the consumption of reactive sites was only 50%. The calculated structure factor indicates a distinct difference between the two simulation states in accordance with the 3D visualization of the system and the box‐counting method.

     

Monitoring Singlet Oxygen and Hydroxyl Radical Formation with Fluorescent Probes During Photodynamic Therapy

Singlet oxygen (¹O₂) is the primary oxidant generated in photodynamic therapy (PDT) protocols involving sensitizers resulting in type II reactions. ¹O₂ can give rise to additional reactive oxygen species (ROS) such as the hydroxyl radical (^?OH). The current study was designed to assess 3′‐p‐(aminophenyl) fluorescein (APF) and 3′‐p‐(hydroxyphenyl) fluorescein (HPF) as probes for the detection of ¹O₂ and ^?OH under conditions relevant to PDT. Cell‐free studies indicated that both APF and HPF were converted to fluorescent products following exposure to ¹O₂ generated by irradiation of a water‐soluble photosensitizing agent (TPPS) and that APF was 35‐fold more sensitive than HPF. Using the ¹O₂ probe singlet oxygen sensor green (SOSG) we confirmed that 1 mm NaN₃ quenched ¹O₂‐induced APF/HPF fluorescence, while 1% DMSO had no effect. APF and HPF also yielded a fluorescent product upon interacting with ^?OH generated from H₂O₂ via the Fenton reaction in a cell‐free system. DMSO quenched the fluorogenic interaction between APF/HPF and ^?OH at doses as low as 0.02%. Although NaN₃ was expected to quench ^?OH‐induced APF/HPF fluorescence, co‐incubating NaN₃ with APF or HPF in the presence of ^?OH markedly enhanced fluorescence. Cultured L1210 cells that had been photosensitized with benzoporphyhrin derivative exhibited APF fluorescence immediately following irradiation. Approximately 50% of the cellular fluorescence could be suppressed by inclusion of either DMSO or the iron‐chelator desferroxamine. Combining the latter two agents did not enhance suppression. We conclude that APF can be used to monitor the formation of both ¹O₂ and ^?OH in cells subjected to PDT if studies are performed in the presence and absence of DMSO, respectively. That portion of the fluorescence quenched by DMSO will represent the contribution of ^?OH. This procedure could represent a useful means for evaluating formation of both ROS in the context of PDT.     

Model liquid crystalline dimers in a slit pore: Monte Carlo simulation study

ABSTRACT

In this work, we present results from (isobaric–isothermal) Monte Carlo Simulation studies of liquid crystalline dimer systems confined in a slit pore. Liquid crystalline dimer systems of various spacer numbers have been considered. Surface-induced conformational and alignment properties of these systems at different pressures under homeotropic anchoring condition have been investigated. We have used easily manageable coarse grained force fields to model both monomer–monomer and monomer–substrate interaction potentials. According to the simulated result, the anchoring of dimers to the surface and orientation of mesogenic units with respect to the surface normal seem to depend on the spacer number for messogen attractive confinement. Dimers with lower spacer number are able be adsorbed to the surface and most of their mesogens are oriented along the surface normal even at lower pressure. Those with larger spacer number are distributed throughout the volume at lower pressure. In the case of mesogen repulsive confinement, most of the dimers are adsorbed to the surface and most mesogens are randomly oriented at low pressure. As the pressure gets higher, the adsorption and orientability increase depending on the type of confinement and spacer number. As a result, clear submolecular partitioning and smectic A like structure have been identified.     

Monte Carlo Simulations of Polymers in Nanoslits

Summary: Monte Carlo computer simulations have been performed for model polymers confined in slits of thickness comparable to the transverse diameter of the chains. The density of polymer within the slits is allowed to vary with the slit thickness in such a way that the content of the slits is always in equilibrium with a large reservoir of bulk polymer. The calculations reveal the presence of polymer‐mediated attractive or repulsive interactions between the slit plates, oscillating with the slit thickness in good agreement with experimental results.

The base cell used in the simulations.